The present invention relates to the processing of gaseous media and in particular to the reduction of the emission of particulate and other materials from the exhausts of internal combustion engines.
One of the major problems associated with the development and use of internal combustion engines is the noxious exhaust emissions from such engines. Two of the most deleterious materials, particularly in the case of diesel engines, are particulate carbon and oxides of nitrogen (NOx) Increasingly severe emission control regulations are forcing internal combustion engine and vehicle manufacturers to find more efficient ways of removing these materials in particular from internal combustion engine exhaust emissions. Unfortunately, in practice, it is found that techniques which improve the situation in relation to one of the above components of internal combustion engine exhaust emissions tend to worsen the situation in relation to the other. Even so, a variety of systems for trapping particulate emissions from internal combustion engine exhausts have been investigated, particularly in relation to making such particulate emission traps capable of being regenerated when they have become saturated with particulate material.
Examples of such diesel exhaust particulate filters are to be found in European Patent Application EP 0 01 0384; U.S. Pat. Nos. 4,505,107; 4,485,622; 4,427,418; and 4,276,066; EP 0 244 061; EP 0 112 634 and EP 0 132 166.
In all the above cases, the particulate matter is removed from the exhaust gases by a simple, physical trapping of particulate matter in the interstices of a porous, usually ceramic, filter body, which is then regenerated by heating the filter body to a temperature at which the trapped diesel exhaust particulates are burnt off. In most cases the filter body is monolithic, although EP 0 010 384 does mention the use of ceramic beads, wire meshes or metal screens as well. U.S. Pat. No. 4,427,418 discloses the use of ceramic coated wire or ceramic fibres.
In a broader context, the precipitation of charged particulate matter by electrostatic forces also is known. However, in this case, precipitation usually takes place upon large planar electrodes or metal screens.
It is known also to remove pollutants from internal combustion engine exhaust gases by establishing an electric discharge in a reactor chamber through which the exhaust gases are made to pass. The electric discharge causes the conversion of the pollutants to less harmful materials, which are discharged from the reactor chamber to the atmosphere. Examples of such devices are given in GB 2 274 412; European Patent Application 0 366 876; OLS DE 3708508; and U.S. Pat. 3,180,083.
However, in the above mentioned systems the high voltages required to excite the electric discharges are generated by power sources which are remote from the devices in which the removal of the pollutants from the exhaust gases is carried out. Not only does this require the use of high voltage transmission systems with their attendant safety implications, but in cases where pulsed dc or ac voltages are used to excite the electric discharges, considerable electromagnetic emissions can occur.
It is an object of the present invention to provide a reactor device especially suitable for the reduction of internal combustion exhaust emissions in which these problems are addressed.
According to the present invention there is provided a reactor for the processing of a gaseous medium, including a reactor bed, means for constraining a gaseous medium to be processed to flow through the reactor bed and a power supply unit adapted to generate and apply a potential across the reactor bed which is sufficient to excite an electric discharge in the gaseous medium flowing through the reactor bed, wherein the reactor bed and the power supply unit are adjacent, directly connected together electrically, preferably co-axial, and preferably are enclosed in an electrically conducting enclosure which is adapted to be maintained at ground potential.
Not only does the grounded enclosure isolate electrically the reactor bed and the power supply unit but it acts as a Faraday cage so as to prevent the emission of electromagnetic radiation when pulsed dc or ac potentials are used to excite the gaseous medium.
Preferably, the enclosure consists of a sealed metal chamber enclosing the reactor bed and the power supply unit.
Preferably the reactor bed consists of a cylindrical body of gas permeable dielectric material contained between two concentric gas permeable electrodes the outer one of which is grounded and the inner one of which is connected directly to the means for generating the said potential.
In a particular embodiment of the invention the reactor chamber is adapted to form part of the exhaust system of an internal combustion engine.